The present invention relates to an improved electronic musical instrument of a wave memory reading type, and more particularly relates to an improvement in the apparatus for reading out musical tone wave shapes stored in wave shape memories so as to generate musical tones which correspond to operated keys of the keyboard of the electronic musical instruments.
The conventional electronic musical instrument of a wave memory reading type generally includes a keyboard circuit having a plurality of output lines which respectively correspond to a plurality of keys, an address signal generator coupled to the keyboard circuit and generative of address signals when any key in the keyboard is operated, and a wave shape memory storing sample values of a wave shape and outputs a musical tone wave shape signal upon receipt of the address signals passed from the address signal generator. Preferably, the musical tone wave shape signal so obtained is multiplied by an envelope wave shape for generation of a corresponding musical tone. The address signal generator in general includes a frequency information memory generative of different frequency information signals when different keys are operated, and an accumulator which sequentially accumulates the frequency information signals at times determined by given clock pulse signals in order to output accumulated values as address signals for the wave shape memory.
With the above-described construction of the conventional electronic musical instrument of a wave memory reading type, the operation of different keys causes generation of different frequency information signals and, consequently, different series of accumulated values which define different series of address signals for the wave shape memory. Therefore, the speed of aligning the values from the wave shape memory differs from key to key when any key is operated. The combination of the sample values read out of the wave shape memory forms a corresponding musical tone wave shape. That is the musical tone wave shape read out of the wave shape memory differs from key to key when any key is operated.
In this connection, however, it should be noted that the sample values read out from the wave shape memory form part of a single predetermined wave shape which is fixed in advance. Consequently, although a difference in the combination of the sample values read out of the wave shape memory may result in some change in the musical tone wave shape read out of the wave shape memory, the musical tone wave shapes cannot be significantly different from the basic wave shape whose sample values are stored in the wave shape memory. In other words, it is quite impossible with the conventional construction of the electronic musical instrument to generate musical tones having different tone colors for different tonal pitches. Thus, musical tones generated by the conventional electronic musical instruments are quite unlike those generated by natural musical instruments.
In addition, the sampling theorem must be satisfied at reading-out of the wave shape memory as hereinafter explained in more detail. This requirement gives limitation to the number of higher harmonics contained in the musical tone wave shapes read out of the wave shape memory. Due to this limitation, it is difficult to generate musical tones with rich tone colors particularly in the bass range. When the sampling theorem is not satisfied, the generated musical tones contain noises caused by generation of reflected frequency-numbers.
Further, since the frequency-number information memory is required to store frequency-number information corresponding to all keys in the keyboard, it is necessary to use a memory of a large memory size, i.e. a large data storing capacity, which is relatively expensive.